The test has been failing infrequently as when we get to the final
barrier (restarted-fifth-removed) the whole test withIn of 40s
has been reached so the last barrier times out right away.
Trying to remove the Thread.sleep and rely on a larger timeout for the
whole test as well as the default barrier timeout of 30s.
* MemberRemoved must be published before MemberUp, e.g. when restarted
in other DC
* remove from failureDetector when receiving gossip with new member,
not only new joining member
* increase timeout in MultiDcSingletonManagerSpec
* the crossDcFailureDetector was not connected to the reachability table
* additional test by listen for {Reachable/Unreachable}DataCenter events in split spec
* missing Java API for getUnreachableDataCenters in CurrentClusterState
